1. Field of the Invention
The present invention relates to coordinate measuring machines which permit determining the location of any desired point on a work piece relative to three mutually perpendicular coordinate axes.
2. Prior Art
In the prior art coordinate measuring machines have been known which utilize probes which are supported on a cantilever arm, and which arms in turn are mounted onto a single granite cross support way or rail. Air film bearing supports are used in such machines and thus are not new. Various uses of air bearings have been advanced over the years.
A typical prior art coordinate measuring machine utilizes a work table having a flat surface, and a rectangular cross section granite rail or way extends across the width of the table surface near the back of the table. This way is mounted securely to the table, and on the way is mounted a support assembly comprising a box surrounding the granite way and supported with respect to the way during use on an air bearing. The support therefore can move transverse to the table along the rail or way in what can be termed the X axis of measurement. This support in turn has a cantilevered arm extending perpendicular to the granite way, and the arm also is made of granite and is generally of rectilinear cross section. A probe support or sleeve mounts over the cantilevered granite arm and is supported with respect to the arm on air bearings for movement along the axis of the arm which is at right angles to the axis of the main support way. This gives movement in the "Y" axis. A probe is mounted to the support on the arm and is movable in a vertical axis with respect to the table surface, or in other words perpendicular to the table surface, and this gives the Z axis movement.
In the prior art X, Y and Z axis measurements have used digital readouts. Generally speaking a digital readout from a reference point is provided, and suitable electro-optical sensors are utilized to provide a pulse each time the respective support moves along its respective axes an increment from the reference point. By suitable digital control equipment, the position of the probe itself can therefore be determined at any given point in all three axes of measurement.
By placing a work piece on the table surface, and identifying a reference point on the work piece, the work piece can be checked for dimensional accuracy; it can be checked to determine that particular features such as a hole are in the exact desired position; and generally the coordinate measuring machine can be used for rapid checking of the position of any point on the work area of the table or on a work piece on the table.